This invention is concerned with a new class of heat engines where the working fluid, for example steam, is used in its two-phase region with vapor and liquid occurring simultaneously for at least part of the cycle, in particular the nozzle expansion. The fields of use are primarily those where lower speeds and high torques are required, for example, as a prime mover driving an electric generator, an engine for marine and land propulsion, and generally as units of small power output. No restrictions are imposed on the heat source, which may be utilizing fossil fuels burned in air, waste heat, solar heat, or nuclear reaction heat etc.
The proposed engine is related to existing steam turbine engines; however, as a consequence of using large fractions of liquid in the expanding part of the cycle, a much smaller number of stages may usually be required, and the turbine may handle liquid only. Also, the thermodynamic cycle may be altered considerably from the usual Rankine cycle, inasmuch as the expansion is taking place near the liquid line of the temperature-entropy diapgram, and essentially parallel to that line, as described below. In contrast to other proposed two-phase engines with two components (a high-vapor pressure component and a low-vapor pressure component, see U.S. Pat. Nos. 3,879,949 and 3,972,195), the present engine is limited to a single-component fluid, as for example water, the intent being to simplify the working fluid storage and handling, and to improve engine reliability by employing well proven working media of high chemical stability.